People Who Drive on Glass Bridges...

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Very soon, bridges will be made of glass. And plastic. And carbon.

Scientists and engineers around the world are working on a new generation of construction materials for bridges that will resist corrosion and last longer with less need for repair. Canada, China, Japan and Scotland are among nations that have built or are about to build bridges using polymer composites. In the near future, the suspension cables, support girders and main deck of many bridges will be made of millions of braided, woven and fused strands of composite materials cooked up in laboratories by engineers.

There's an international race to develop these materials because bridges everywhere are crumbling from the effects of weather, pollution and age, says John Scalzi, a structural engineer who directs the National Science Foundation (NSF)'s Large Structural and Building Systems Program. Scalzi says the United States, which has lagged dangerously behind, urgently needs to catch up with advances in construction materials achieved in other countries for at least two reasons:

First, he says, the civil infrastructure in the U.S. is in bad shape. The Federal Highway Commission reports that 42 percent of bridges need repair and are obsolete; the cumulative repair bill by the year 2010 is estimated to reach $50 billion. New, low-maintenance materials are needed immediately to repair a long list of existing bridges in every state of the union.

Second, on the global scale, the nations with the most advanced design and manufacturing programs will dominate the world export market for the new polymer materials.

On Scalzi's desk lies a stack of 18-inch rods in various colors and shapes. They are samples of new building materials under development in university laboratories through projects underwritten by NSF grants. If the rods were made of standard metal alloys, they would weigh twice as much. Multiplied by miles of rods and cables that go into a two-to-four-lane bridge, the weight reduction means a significant contribution to the long life of a structure. Also, metal rods imbedded in concrete for reinforcement age and corrode over time from exposure to the acidic concrete and moisture collecting in the cracks, whereas plastic and glass fiber rods are expected to last 10 to 100 times longer without maintenance.

The current research in polymer composite materials grew out of earlier aerospace efforts to find radar-evading "stealth" materials, says Scalzi, "which is a perfect example of military research spinning off into unforeseen civilian uses." He says continued research into new uses for these polymers will not only lead to better bridges, roads and buildings, but along the way provide new, diversified commercial ventures for the struggling aerospace firms that first developed these materials.

Nearly 40 laboratories across the U.S. are developing and testing these new materials through programs underwritten by NSF. They include:

California State University at Long Beach: developed synthetic cables to be installed on a suspension bridge, and composite materials for a deck on another bridge. Contact: Joseph Plecnick, professor of civil engineering (310) 9854406.

Catholic University (Washington, D.C.): preparing to monitor and evaluate a new grid system it developed for a full scale bridge deck to be constructed in Washington, D.C., in 1996, using new fiber-reinforced plastic materials. Contact: Lawrence Bank, professor of civil engineering (202) 319-4381.

Finally, here's an example of how this emerging technology is now in use:

E.T. Techtonics of Philadelphia, Penn., constructs and installs pedestrian and equestrian bridges using polymer technology especially desirable in remote and ecologically sensitive areas such as national parks. The technology was tested with an NSF small business grant. Contact: G. Eric Johansen, company president (800) 854-0957.

The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2017, its budget is $7.5 billion. NSF funds reach all 50 states through grants to nearly 2,000 colleges, universities and other institutions. Each year, NSF receives more than 48,000 competitive proposals for funding and makes about 12,000 new funding awards.